1. Field of the Invention
The present invention relates to a process for producing carboxylic acid esters from nitriles. More particularly, it relates to a process for converting nitriles to carboxylic acid esters in high yields by the vapor phase catalytic reaction of the nitrile, water and alcohol in the presence of a titanium containing oxide catalyst prepared in a specific manner.
2. Description of the Prior Art
Esters, especially acrylic acid esters, methyl methacrylate, etc. are very useful materials from an industrial point of view. For example, acrylic acid esters are widely used in fibers, paints, adhesives and methacrylic acid esters are used as starting materials for synthetic resins. A liquid phase process as disclosed in Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Ed. (1965), Vol. 8, pages 339 to 340, and Finar, I. L., Organic Chemistry, Longmans, Publ. (1963), page 295 is commonly used for producing these carboxylic acid esters in which a nitrile is used as a starting material in the presence of a catalyst such as sulfuric acid or hydrochloric acid in liquid phase. When producing acrylic acid esters from acrylonitrile, acrylonitrile, alcohol and sulfuric acid are reacted in liquid phase. Such a process comprises producing acrylamide sulfate from acrylonitrile, sulfuric acid and water and subsequently adding an alcohol thereto to produce acrylic acid ester, but this process has the disadvantage that the reaction must be conducted in two stages. In addition, because the amount of sulfuric acid used must be equimolar or more than the acrylonitrile and highly concentrated sulfuric acid is applied at elevated temperatures, special consideration is needed for the selection of the materials for the reaction apparatus. Further in this process, there are problems such as a reduction in yield due to side reactions such as polymerization, production of a large amount of economically disadvantageous ammonium sulfate and the like.
A process for producing carboxylic acid esters by the vapor phase catalytic reaction of nitriles with water and alcohol in the presence of a catalyst has been proposed to eliminate the above problems. For example, U.S. Pat. No. 2,913,486 discloses a process for producing methyl acrylate, methyl methacrylate, etc. from unsaturated aliphatic nitriles using a solid esterification catalyst such as silica, silica alumina, titania, zirconia or thoria. U.S. Pat. No. 3,466,320 discloses a process for producing unsaturated aliphatic acid esters from the corresponding unsaturated nitriles using an esterification catalyst containing niobium pentoxide, and Japanese Patent Application (OPI) No. 25120/72 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application".) discloses a process for producing acrylic acid esters from acrylonitrile using a catalyst containing boron trioxide. In these processes carboxylic acid esters are produced from nitriles in one stage, and although there was no need to use sulfuric acid unlike the conventional process, the percent conversion to the carboxylic acid esters from the nitriles is only about 10% and thus these processes are not satisfactory from the standpoint of the catalytic activity. This indicates that while conventional solid esterification catalysts exhibit catalytic activities that provide esters in theoretical yields in the reactions of organic acids and alcohols, they do not have sufficient catalytic activities for the reactions of nitriles and alcohols.